Recent years, a water closet of a type designed to be fluidically connected directly to a water system, such as a city water line, and fed with flushing water directly from the water system has come into wide use. In this type of water closet, a water system and a line for supplying flushing water to a bowl are in direct fluid communication with one another through a water-feed valve. Therefore, there is a conceivable risk that a negative pressure generated in the water system from some cause, such as cut-off of water, causes a backflow of flushing water from the water closet to the water system. In order to avoid such a risk, this type of water closet is equipped with a vacuum beaker for eliminating the backflow. Japanese Patent Laid-Open Publication No. 2001-182122 discloses a flushing-water feed device provided with a vacuum breaker disposed on a downstream side of a water-feed valve so as to eliminate such a backflow. This vacuum breaker is operable, when water is permitted to pass through the water-feed valve (in a flow state), to provide fluid communication between the water-feed valve and a flushing-water supply line to a water closet, and, when water is inhibited from passing through the water-feed valve (in a non-flow state), to open the flushing-water supply line to ambient air. In the water closet equipped with this vacuum breaker, the flushing-water supply line is opened to ambient air in the non-flow state, and, in the event that a negative pressure is generated in the water system, the ambient air is taken into the water system to eliminate the risk of backflow of flushing water from the supply line to the water system.
Patent Publication 1: Japanese Patent Laid-Open Publication No. 2001-182122